The dual operator[] idiom

• It's common to define two operator[]s

• Allows use on left hand side, as well as on const objects:

  template< typename ElementT >
  class MyArray {
  public:
      ElementT& operator[](unsigned int idx);
      ElementT operator[](unsigned int idx) const;
      //...
  };//class MyArray
  void copy_element( unsigned int idx, MyArray<int> const& src, MyArray<int>& dest )
  {
      // Uses non-const op[] on left, const op[] on right:
      dest[ idx ] = src[ idx ];
  }
  void main()
  {
      MyArray<int> source;
      MyArray<int> destination;
      //...
      copy_element( 0, source, destination );
  }